I quit! What carb do I have??? 9.9 or 15???

[BlackoutBill21]

Ok gurus. I give. 20 hoUrs + of research and I’m more lost as ever...

my 9.9 runs like crap.... idles great but won’t go above 3000 rpms.

Now im singlinging it out to a carb issue before i go further... however....

i have NO idea what the previous owner did to this thing...

all indications lead me to believe it’s a 9.9 carb. But signs points to possible 15. I can’t find my part number ANYWHERE! And don’t have calipers to measure throat diameters.

I know for for a fact it had a #54 orface plug which indicates a sel sail boat model carb.

bought and replaced it with proper 50. Still ran like crap.

Its an 1988 with plastic top and bowl.

engraved on the upper carb itself is mx436989

upper plastic cover says 436949

bowl says340182

if if I can just get an actual answer to whichbcarb I have, I’ll buy another from eBay and see if my symptoms are the same. Then I can investigate further.... PLEASE PLEASE PLEASE SOMEONE have the kowlege im
missing

 

[oldboat1]

9.9 sailboat carb (e.g. '82 Yachtwin) has the larger throated carb -- 15 body. Probably not your rpm issue, though. Check compression. And might need to reprop based on hull size/weight.

 

[BlackoutBill21]

Compression is 120 each cylinder... I re cleaned the carb and installed a previously missed gasket... runs better: fantastic in the barel. But.... wants to die out unless I SLOWLY raise the throttle. If I gun it/ it will stall. Tach says 5000 before I have to stop cause too much water leaves the barrel.

 

[oldboat1]

Good compression. My '82 is about there (123 or so). Try bumping the idle mix needle a little richer (c.clockwise 1/8 turn at a time) -- affects throttle up.

 

[BlackoutBill21]

It’s a deep V HULL, and lightweight. Checked to make sure prop wasn’t spun and it’s ok. I only hit 4 mph... I know it’s not gunna be crazy fast... but 4mph??? I hit 20 mph with an 18 hp earlier this year

 

[BlackoutBill21]

Thanks old boat. I’ll try that but I’ve had the needle every which position going... seems to idle best at 3 turns out

 

[flyingscott]

A 9.9 carb has a tube that runs right through the middle of the venturi. A15 hp will not have that. Have you looked at the fuel pump?

 

[BlackoutBill21]

New fuel pump... I’ve seen pictures of 9.9 carbs with that tube that does not go through to the top. Mine only goes half way up. I mean it’s in the middle but it stops close to the butterfly valve...

 

[tomhath]

It's simple to verify that you have spark on both cylinders, just pull one spark plug wire at a time to see it anything changes. It will start and run fine on one, just lacks power.

 

[BlackoutBill21]

I will try that tomorrow Tom thanks

 

[BlackoutBill21]

[No message]

 

[flyingscott]

That is a 15 hp carb.

 

[BlackoutBill21]

I’m not being a ****... seriously??? Your 100% sure? I just swapped out the 54 stamped oraface plug for the 34 and it’s running better.... I’m so lost

 

[MTboatguy]

I’m not being a ****... seriously??? Your 100% sure? I just swapped out the 54 stamped oraface plug for the 34 and it’s running better.... I’m so lost

I am sure, I have two of them out in the shop sitting on the bench, that is a 15 carb....need to track down the complete carb and then start at the beginning to get it to run correctly.

 

[BlackoutBill21]

Ok I see it! Def 15! Ok step 2... the original oraface plug that was in it was stamped 54. I’m told that’s not suposed to be right. I ordered the #55 from eBay. Once installed if it’s still acting the same I will do a running spark test, and then get a new prop? Where do I start with props??

 

[BlackoutBill21]

Thanks again MT

 

[flyingscott]

Why would you swap a 54 orifice for a 34? The factory specs a 50 orifice for a 9.9 motor.

 

[BlackoutBill21]

I’m sorry yes it was a 50 that I put In it. But since it’s a 15 I’ll install the 55 when it comes in

 

[Tim Frank]

Refer to this thread....sounds similar.
#50 is wayyyy too big. #55 is bigger still.
Sounds like someone was looking for that pot of gold at the end of the rainbow....throwing some parts at a 9.9 HP and waving a magic wand.....hoping for 15HP

https://forums.iboats.com/forum/engi...-over-3000-rpm

 

[oldboat1]

50 for the '88 9.9, 54 for the 9.9 Yachtwin, 55 for the 15. A 54 or 55 should be correct for your carb.

I don't think you've posted a model number. '88 9.9 Yachtwin would be E10SELCCD (equipped with the 54 orifice). If you have an '88, it's also possible somebody converted the sailboat model to a shorter shaft.